Semiconductor manufacturing is broadly divided into three areas, material, preparation and design, for example, designing the circuits to be fabricated, preparing photolithography masks and making raw wafers, and wafer processing, for example constructing circuits into the wafer and assembly, packaging and testing, for example which packages and tests each individual circuit.
Production planning is the process of choosing objects to be started and to be worked in a manufacturing facility during some future time period or time interval in accordance with a plan so that performance is maximized. These objects are usually selected from a variety of product types which may require different resources and serve different customers. Therefore, the selection of the object must optimize customer-independent performance measures such as cycle time and customer-dependent performance measures such as on-time delivery.
The reasons for requiring advance production planning may be unique to each manufacturing facility or factory. For example, one facility may require advanced planning so that materials may be ordered and delivered in time for the manufacturer. Another facility may require advanced planning to make delivery commitments to customer or predict delays in delivery of the product, namely the object.
To configure a production plan which yields the best performance, the capacity, or amount of work the facility can complete must be modeled in some fashion, since planning objects to be worked when the capacity of the facility has been reached compromises performance and yields no positive benefits.
The production plan usually entails construction of schedules of the objects to be worked to govern the production of orders of the objects in the job shop or facility. The construction of schedules to govern the production of orders in a facility is a complex problem that is influenced by knowledge or information accumulated from many different sources within the facility. The acceptability of a particular schedule or plan depends upon diverse and conflicting factors such as due date requirements, cost restrictions, production levels, machine capabilities and substitutability, alternative productive process, order characteristics, order requirements and resource availability.
One prior technique uses a purely predictive approach to scheduling, based on a restricted model of the environment; predictions are made as to when operations are to be performed The resulting schedules or plan often bear little resemblance to the actual state of the factory, leaving detailed schedules to the shop-floor supervisor.